Hydrogen has been attracting attention as an energy source enabling reduction of carbon dioxide emissions. There is, however, a risk of explosion of hydrogen gas that has leaked into an atmosphere (around a hydrogen gas production apparatus or a hydrogen gas storage apparatus, in a car park for hydrogen-fueled vehicles, etc., for example). Thus, it is necessary to quickly detect a hydrogen gas leak and stop it.
In this connection, hydrogen sensors for detecting hydrogen gas have been developed, one of which is shown in Japanese Unexamined Patent Publication No. 2005-083832 (Patent Document 1), for example. As shown in FIG. 8, this hydrogen sensor 10′ has a light control film (reflecting film) 14 consisting of a thin film layer 12 and a catalyst layer 13, formed on a top surface of a light-transmitting member 11 of glass or the like. At normal temperature, when contacted by hydrogen gas in an atmosphere, the catalyst layer 13 quickly causes reversible hydrogenation of the thin film layer 12, thereby causing a change in optical reflectance of the thin film layer 12.
FIG. 9 shows a schematic structure of a hydrogen gas detecting apparatus 20′ using such hydrogen sensor 10′. As shown in FIG. 9, in the hydrogen gas detecting apparatus 20′, light 21a from a light source 21 is reflected by the light control film 14 of the hydrogen sensor 10′, and the reflected light is received by an optical sensor 22. A hydrogen gas leak can be detected from a change in the amount of reflected light received by the optical sensor 22.
In this hydrogen gas detecting apparatus 20′, light 21a from the light source 21 travels in the atmosphere and arrives at the optical sensor 22. Thus, there is a possibility that light from a light source other than the light source 21 (disturbance light from an illumination lamp at the ceiling of an underground car park, a headlight of a vehicle or the like, for example) is received by the optical sensor 22, or undergoes reflection or the like at the hydrogen sensor 10′ and is received by the optical sensor 22. There is also a possibility that suspended dust in the optical path from the light source 21 to the hydrogen sensor 10′ or in the optical path from the hydrogen sensor 10′ to the optical sensor 22 prevents the optical sensor 22 from receiving light. There is also a possibility that dust or the like covers the hydrogen sensor 10′ and prevents the optical sensor 22 from receiving light.
The hydrogen gas detecting apparatus 20′ detects a change in transmittance caused by hydrogenation only in a narrow area (almost a point) of the hydrogen sensor on which light 21a is thrown. Thus, the hydrogen gas detecting apparatus 20′ has room for improvement in hydrogen gas sensitivity.